Image orthicon with magnetic focus

ABSTRACT

An image orthicon tube is provided with a photocathode and a target spaced therefrom. Interposed therebetween is an accelerating electrode and a further electrode interposed between the accelerating electrode and the photocathode. The accelerating electrode is supported opposite the photocathode by a distance equivalent to the longitudinal length of the further electrode. The further electrode is maintained at the same potential as that of the photocathode.

United States Patent [72] inventor Ljubov Dmitricvna Axenova 2,618,761 11/1952 Rose 313/65 X Pros-pelt! Morin Toreza, 38, Korpus 4, kv. 3,213,308 10/1965 Feibelrnan 313/65 [2 A l N gg zg FOREIGN PATENTS PP r [22) Filed Aug 14, 1968 135,511 1/1959 U.S.S.R. .1 313/65 T [45] Patented Aug. 10, 1971 Primary ExaminerRobert Sega] At!0rneyWaters, Roditi and Schwartz [54] IMAGE ORTHICON WITH MAGNETIC FOCUS 2 Chhas, 3 Drawing Figs.

U.S. An image orthicon tube is provided a 313/ 8475313435 photocathode and a target spaced therefrom. lnterposed Y M1101] therebetween is an accelerating electrode and a further elec- 1 trode interposed between the accelerating electrode and the [50] hoto athode The accelerating electrode is upported 0pposite the photocathode by a distance equivalent to the lonlsfi] Rum CM gitudinal length of the further electrode. The further electrode UNITED STATES PATENTS is maintained at the same potential as that of the 2,487,665 1 1/ 1949 Morton et al 313/65 photocathode.

IMAGE ORTHICON WITH MAGNETIC FOCUS The present invention relates to television camera tubes of the image orthicon type.

At present, wide use is made of the image orthicon, a television camera tube whose evacuated envelope houses a photocathode where an optical image of the scene being televised is produced. The photoelectrons ejected by the photocathode are caused to move by an accelerating electric field and a focusing magnetic field within the image-transfer (photocathode-to-target image) section towards a target to form an electron pattern which is a replica of the optical image projected onto the photocathode. Further conversion of an electron image into a video signal is performed by a scanning-beam section.

In the image-transfer section of such a television camera tube, the magnetic lines of force are out of register by a considerable amount with electron trajectories in the electric field, so that the image is considerably out of focus at the edges and is subject to spiral distortion. The resolution is thus greatly impaired, and geometrical distortion is inevitable.

An object of the present invention is to provide for a more uniform resolution over the entire electron image and reduced geometrical distortion.

This and other objects are accomplished by an image orthicon-type television camera tube in which, according to the invention, there is an additional cylindrical electrode in the image-transfer section, placed between the photocathode and the accelerating electrode, arranged coaxially with the latter and held at the potential of the photocathode, the accelerating electrode being separated from the photocathode by a distance approximately equal to the length of the additional electrode.

It is preferable to make the additional cylindrical electrode integral with the photocathode, for example as a deposit on the faceplate of the evacuated envelope, directly connected to the photocathode.

An advantage of the image-orthicon tube herein disclosed resides in that the installation of an additional cylindrical electrode produces in the focusing electric field near the cathode an area such that the electrons in that field are caused to fol-' low trajectories which are closer to the magnetic lines of force, with the result that there is a marked improvement in the resolution at the edges of the image and in its geometry.

The invention will be more fully understood from the following description of a preferred embodiment when read in connection with the accompanying drawings wherein:

FIG. 1 illustrates an image orthicon-type television camera tube, according to he invention, showing the image-transfer (Photocathode-to-target image) section and the focusing coil;

FIG. 2 is a map of equipotential lines in the electric field and electron trajectories in an image orthicon-type television camera tube, according to the invention; and

FIG. 3 is a map of equipotential lines in the electric field and electron trajectories in existing image orthicons.

According to the present invention, there is provided an image orthicon-type television camera tube comprising an evacuated envelope 1 (FIG. 1), with an image-transfer (photocathode-to-target image) section incorporating a photocathode 2 on which the image to be televised is projected optically, an accelerating electrode 3, a cylinder 4 with a target 5. The image-transfer (photocathode-tmtarget image) maintained at the same potential.

With the electrodes of an image orthicon-type television camera tube arranged as described above, the equipotential lines of the electric field will be distributed as shown in FIG. 2, and an electron ejected in a direction normal to the surface of the photocathode 2 and moving solely in the electric field will follow a trajectory shown by the curve 8. In the plane of the target the deflection of this trajectory from a line of force 9 due to the focusing magnetic field is 01,.

In existing image orthicons the equipotential lines of the electric field are distributed as shown in FIG. 3, and the deflection of the trajector represented by the curve 10 from the line of force 9 due to the focusing magnetic field in the plane of the target 5 is 0:

From a comparison of FIGS. 2 and 3, one may conclude that the deflection (1,.

From a comparison of FIGS. 2 and 3, one may conclude that the deflection a is much smaller than the deflection 01,, and that in an image orthicon-type television camera tube made according to the invention both the amount of outoffocus and geometrical distortions are less pronounced than in existing image orthicons.

The image orthicon-type television camera tube herein disclosed offers improved performance, has the same overall dimensions and operating voltages as conventional image orthicons, and may, therefore, be employed in conventional apparatus without any modifications in the latter.

I claim:

1. An image orthicon-type television camera tube comprising an evacuated envelope; a photocathode supported by said envelope and on which a scene image to be televised is projected optically; said photocathode being maintained at a prescribed potential; a target on which an electron image of the scene is formed, said target being spaced from said photocathode; an accelerating electrode interposed between said photocathode and said target; magnetic means supported externally of said envelope for magnetically focusing photoelectrons from said photocathode on said target; an additional cylindrical electrode maintained at said prescribed potential of said photocathode and interposed between said photocathode and said accelerating electrode, coaxially with and annularly spaced from the latter so that the distance between said photocathode and said accelerating electrode is substantially equal to the longitudinal length of said additional cylindrical electrode said additional cylindrical electrode including an open end portion annularly spaced from said accelerating electrode and an opposite end portion integral with said photocathode.

2. An image orthicon tube as claimed in claim 1 wherein said magnetic means is a coil surrounding said evacuated envelope. 

1. An image orthicon-type television camera tube comprising an evacuated envelope; a photocathode supported by said envelope and on which a scene image to be televised is projected optically; said photocathode being maintained at a prescribed potential; a target on which an electron image of the scene is formed, said target being spaced from said photocathode; an accelerating electrode interposed between said photocathode and said target; magnetic means supported externally of said envelope for magnetically focusing photoelectrons from said photocathode on said target; an additional cylindrical electrode maintained at said prescribed potential of said photocathode and interposed between said photocathode and said accelerating electrode, coaxially with and annularly spaced from the latter so that the distance between said photocathode and said accelerating electrode is substantially equal to the longitudinal length of said additional cylindrical electrode said additional cylindrical electrode including an open end portion annularly spaced from said accelerating electrode and an opposite end portion integral with said photocathode.
 2. An image orthicon tube as claimed in claim 1 wherein said magnetic means is a coil surrounding said evacuated envelope. 